What are quantum materials and why are quantum materials important?

From stones to qubits: Welcome to the age of quantum materials!

The Border Between Classical and Quantum Worlds: When Does Physics Go Quantum?

The Quantum Evolution: Quantum Mechanics Developed Just Like Quantum Mechanics Works

(General Discussion) Human history can be described in terms of materials and their use for the development and destruction of society (yes! Of course). In the Stone Age, we learned to use stone tools for hunting, developed cool cave apartments, scratched cave walls to make symbols, children of the current generation still do this at relatives’ house. In the Bronze Age, we switched from throwing stones to throwing bronze weapons. With the rise of sharp bronze weapons, urban civilizations expanded and trade networks began to flourish. The Iron Age is the advanced age with more robust weapons, thus new kingdoms began to flourish and started taking over the lands of neighbours (golden age for land mafia). In the Silicon Age, we started making silicon chips and created computers, which accelerated the development of society in all possible aspects. As humans we still love to hunt, but now we do it with just thumb and finger on the screen (really!!). The polymer/plastic era has made the world lighter, cheaper and flexible (plastic is everywhere – confirmed by a fish in the sea). Great!

So what is the state of affairs in terms of materials now? What era are we living in in terms of materials in 2025?

(Quantum materials) In last a few decades, there has been discovery and synthesis of a new class of materials that has astonishing properties but that could not be fully explained by the laws of classical physics. These properties can only be explained by quantum mechanics. These are the materials of interest and called quantum materials. Just to rephrase, quantum materials are the materials that follow quantum mechanics laws and their astonishing behaviours can not be fully explained by classical physics.  

To make things more clear, the properties of every materials can be explained by quantum mechanics but not all materials are called quantum materials . At large scales (when the size of matter is large), quantum mechanics and classical mechanics predict the same results. But as we move the size to microscopic level (e.g. 1000 times smaller than the thickness of our hair), where we start restricting the motion of electrons in a matter, due to quantum confinement effects, we see new phenomena that cannot be fully explained by classical mechanics.

Also, at low temperatures, the electronic properties of some materials changes drastically that cannot be addressed by classical mechanics. So what exactly happens?

Why Do Quantum Materials Show Phenomena That Don’t Appear at the Bulk Level?

A lot of things change at the microscopic/quantum scale (say nanometers or below). At this scale, every electron has the power to change the property of the material. It’s similar to the situation where whispering in a crowded space (say at bulk scale) cannot be heard, but whispering becomes audible when the crowd noise fades away. At the bulk level, the properties of trillions of electrons average out. But when we scale down, every electron is “heard.”

In classical materials, response of a material can be recorded either in 1 (ON/TRUE/YES) state or 0 (OFF/FALSE/NO) state. But in quantum materials, system can be in many states; 0, 1, and everything in between at the same time. This fundamentally changes the properties of the materials.

Key reasons for the quantum phenomena in quantum materials

(a) Wave-like behavior
Instead of showing particle-like behavior, electrons show wave-like behavior at the quantum scale. So we start seeing interference, diffraction, etc. wave-like properties in quantum materials that cannot be observed at the bulk scale.

(b) Quantum confinement
When we restrict electrons into tiny spaces, where they cannot move freely in all degrees of freedom, their energy levels get quantized. This is similar to piano strings, which have specific sounds for each string but cannot make sounds in between. Similarly, the energy levels of electrons get quantized, and there are specific energy band gaps that cannot be occupied by electrons. This can change electrical, optical, and other properties.

(c) Surface effects
In bulk, the surface to volume ratio is very small. But at the nano scale, the surface to volume ratio is very high, and surface atoms dominate the behavior of the material. This makes the material more reactive, tunable, and sensitive.

(d) Electron correlation
At small scales, electrons interact more strongly with each other. This could lead to a zero resistance state in materials (superconductivity), never freezing spins of the electron (quantum spin liquids), etc.

(e) Topological effects
Topological effects can also emerge in quantum materials, where the surface conducts but the interior part of the material remains insulating like in topological insulators.

Why quantum materials are important and what technologies can they bring?

Quatum materials are important because they open up possibilities that classical materials simply can’t!  I will give some examples of quantum materials that leads to the quantum technologies (there are more quantum materials than those reported here!!!).

1.  Superconductors

These materials can carry electricity without any resistance. Normally, when electricity flows through a wire, some energy is lost as heat due to resistance. But in a superconductor, electrons form pairs that move in perfect harmony, like synchronized swimmers, allowing current to flow with zero energy loss. This has a potential application in Power grids, where power lines could eliminate the electrical losses. Superconductors are also being used in Maglev trains and MRI machines.

2. Topological Insulators

These materials show electrical conductivity on the surface but are insulator in bulk. The conduction is topologically protected and can not be deformed by any defects and hence have great potential in Fault-tolerant quantum computers and low power electronics.

3. Quantum Spin Liquids

These are the materials in which spin of the electrons never freezes even at absolute zero. They show  long range entanglement between spins, meaning measuring one spin instantly affects distant ones, a hallmark of quantum entanglement , which makes them a good candidate  for the development of fault-tolerant quantum computers.

4. Spin Ice

In spin Ice materials, the magnetic moments of the atoms are arranged similarly to protons in water ice, leading to emergent magnetic monopoles. Magnetic monopoles could open up new technologies never seen before.

5. 0D materials

In 0D materials, electrons are confined in all the three directions and are forced to stay at a position. This results in quantization of the energy level. A good example of 0D materials is quantum dot. These materials find applications in LEDs, and displays e.g., QLED, ultra sensitive sensing in medical and environment fields.

6. 1D materials

1D materials are the materials in which electrons can move only in one direction, e.g., quantum wire. These materials are useful for single photon emitters, laser applications, nano-sensors etc.

7. 2D materials

These are one atom thick materials, which shows astonishing properties like quantum Hall effect, fractional quantized conductance. 2D materials have great potential applications in flexible electronics, spintronics, photodetectorsetc.

8. Mott Insulators

In these materials, electrons have very strong interactions. They should conduct but become localized in space and stop conducting due to strong columbic intercations. These materials can find its application in next generation transistors.

9. Weyl and Dirac Semimetals

In these materials, quasiparticle behave like relativistic fermions. These materials are useful in advanced magneto transport applications.

10. Charge Density Wave (CDW) Materials

These kinds of materials exhibit a density wave where electrons form periodic spatial modulations. This can produce ultrafast switches and memristors.

To summarize these in a table:

Category	Properties	Example Materials	Applications
Superconductors	Zero electrical resistance at low temperatures	YBCO, Nb, Fe-based SCs	MRI, power grids, Maglev trains
Topological Insulators	Conducts on the surface, insulates inside	Bi₂Se₃, Sb₂Te₃	Low-power electronics, Fault-tolerant quantum computing
Quantum Spin Liquids	Electron spins never freeze into a pattern	α-RuCl₃, Herbertsmithite	Fault-tolerant quantum computing
Spin Ice	spins mimic proton disorder in water ice	Dy₂Ti₂O₇, Ho₂Ti₂O₇	Quantum memory, analog simulations of magnetic monopoles.
0D Materials	electrons are confined in all three dimensions	CdSe quantum dots, PbS, InAs dots	Quantum LEDs, bio-imaging, quantum computing
1D Materials	electron motion is restricted in two and free in one dimension	Carbon nanotubes, nanowires,	High-speed electronics, nanosensors, energy harvesting
2D Materials	One-atom-thick materials, where electron motion restricted in one dimension	Graphene, MoS₂, WSe₂	Flexible electronics, spintronics
Mott Insulator	insulating due to strong interactions	V₂O₃, NiO, Cu-based oxides	Strongly correlated systems, next-gen transistors
Weyl Semimetals	Exotic quasiparticles that behave like relativistic particles	TaAs, NbAs	Advanced transistors, fundamental physics
Charge Density Wave (CDW) Materials	electrons form periodic spatial modulations	NbSe₂, TaS₂, K₀.₃MoO₃	Memristors, ultrafast switches.

There are some challenges in bringing all the above quantum materials to the realization level in applications due to the special requirements of the conditions in which these quantum phenomena emerge. For instance, superconductors need low temperatures; spin ice and quantum spin liquids are still in developing phase. 2D materials are not scalable yet, and some phenomena need strong magnetic fields, etc. But the time is not far, future is coming at a faster rate. We will see all these materials implemented soon; scientists are working their level best. Microsoft has already made a topological quantum computer. Others are also on the way. It’s just a matter of time.

To stay updated about these upcoming quantum technologies, stay tuned to NewWaveParticle! Subscribe for immediate updates.